120 • IOWA ACADEMY OF SCIENCES. 



ON THP] OCCURRENCE OF RHIZOPODS TN THE 

 PELLA BEDS IN IOWA. 



BY J. A. UDDEN. 



In Jefferson county the Pella beds of the Saint Louis 

 formation have a thickness of about twenty feet. They 

 consist of heavy ledges of calcareous limestones, inter- 

 bedded with seams of marly shales, the latter being best 

 developed in the upper part of the section. The several 

 seams and ledges appear quite persistent and some have 

 been identified at different points a few miles apart. They 

 have evidently been laid down at some considerable 

 distance from the shore. Occasionally there are ledges of 

 limestone which are very fine-grained, almost litho- 

 graphic in texture. Here as elsewhere in the south part 

 of the state, the fauna of the formation is meager in 

 ■species but quite prolific in individuals. Pugnax ottunnva, 

 Spirifer keohd-, Zaphrentis pallaensis, Anisotrypa fistulosa, 

 und stems of crinoids appear everywhere, especially in the 

 marls. This has long been known. 



A closer examination of these rocks shows that some 

 rhizopods also are almost invariably present. By crushing, 

 washing and sifting, these may be found in the marls and 

 sometimes also in the limestone. The most common form 

 has been identified by Schuchert as Endothyni haileyi Hall, 

 which is known from Indiana and Illinois. But there are 

 at least two or three other forms not yet identified. 

 Associated with these are two ostracods: CythercUina 

 glamlulosa and Leperditia carhonaria, and also some minute 

 spines and plates of an Archaeocidaris [very rare]. The 

 presence of the rhizopods corroborates the view that the 

 Pella beds were laid down some distance out in the open 

 sea. 



